User's Guide 03:01 Dependency Injection

If you're using Typescript, you've probably already been warned that this is coming, but, yeah--TaskBotJS supports (one could say "mandates") that you as a developer consider the dependencies for your job. It is totally possible to just use global variables or singletons imported out of other files, but I hope that you won't. And I hope that for a couple reasons:

• It is way harder to build a job which you can test by injecting/mocking dependencies like database connections, API clients, and the like.
• It's more difficult to understand what the external dependencies of a given piece of code are in the case of refactors and the general process of understanding what any given part

Using this is easy. If you're using JavaScript, you just pass a function to your Config object. That function takes as arguments a Bunyan logger and a TaskBotJS client (conventionally called taskbot), then returns an object that can be any object that contains at least those fields. The default implementation of your dependencies provider is pretty easy:

(baseLogger, taskbot) => ({ baseLogger, taskbot })

It's not that much more complicated to use in TypeScript--implement or extend the IDependencies interface and pass in a function that conforms to DependencyFactory<TDependencies> and you're done.

TypeScript heads will probably notice that this isn't a cure-all solution to all your woes. You have some wink-wink flexibility when using JavaScript, but all jobs implemented in TypeScript have to implement Job<TDependencies> with the same generic argument. Which is kind of a bummer, as it would be nice to be able to declare them with different sets of dependencies and be both typesafe and clever about it. On the future roadmap for a later major release of TaskBotJS is to do exactly that. However, in the interim, hey--we've at least made our code explicit and more easily testable. Baby steps!